ZEBRAFISH as DEVELOPMENTAL MODEL 2 Zebrafish Danio rerio

ZEBRAFISH as DEVELOPMENTAL MODEL

2

Zebrafish (Danio rerio) • A tropical fish native to southeast Asia. Popular aquarium fish. • About 2. 5 cm to 4 cm long • Males are slender and torpedoshaped usually with a pink or yellow tinge. • Females tend to be less pink than the males and are fatter due to the eggs they carry.

Zebrafish • In its larval stages it is transparent. As it matures to an adult it develops stripes that run along the length of the body and look blue in colour. • Aided by the transparency of the embryo, if researchers modify the fish's genotype at the egg stage, they can see resulting changes in organ shape or dynamics barely three days later.

Zebra Fish Life Cycle : Time taken

ZEBRAFISH Produce 200 -300 fertilised eggs every week; an ideal attribute for genetic studies § Embryos can be microinjected with m. RNA or DNA corresponding to genes of interest handing down injected gene to next generation § v PRESENT§ Dimethyl-prostaglandin E 2 (dm. PGE 2) increases the number of blood stem cells in zebrafish embryos and stem cells in human cord blood samples 7

ZEBRAFISH § § Large numbers of mutations disrupt embryonic development in zebrafish, serve as models for human diseases like muscular dystrophy, neurodegenrative diseases Leflunomide is in early phase clinical trials to kill melanoma cells. v FUTURE§ Creation of a transparent version of adult zebrafish. Behaviour of tumour cells can be followed like the birth, growth and spread of tumours can be scrutinised § As a disease model for Tuberculosis because zebrafish embryos are transparent, infection with fluorescently-labelled tuberculosis bacteria. 8

Zebrafish as a Developmental Model Organism: Why? Used for mapping and identifying genes involved in organ development. Excellent model for studying infectious diseases v Reasons : 1) The zebrafish is small and robust. 2) Cheaper to maintain than mice. 3) Break of daylight triggers mating in zebrafish (many other fish only lay eggs in the dark). 4) Zebrafish produce hundreds of offspring at weekly intervals providing scientists with an ample supply of embryos to study.

5) They grow at an extremely fast rate, developing as much in a day as a human embryo develops in one month. 6) As zebrafish eggs are fertilised and develop outside the mother’s body it is an ideal model organism for studying early development. 7) Zebrafish embryos are nearly transparent which allows researchers to easily examine the development of internal structures. Every blood vessel in a living zebrafish embryo can be seen using just a low-power microscope.

8) As a vertebrate, zebrafish has the same major organs and tissues as humans. Their muscle, blood, kidney and eyes share many features with human systems. 9) Zebrafish have the unique ability to repair heart muscle. For example, if part of their heart is removed they can grow it back in a matter of weeks. Scientists are working to find out the specific factors involved in this process to see if this will help us to develop ways of repairing the heart in humans with heart failure or who have suffered heart attacks.

Zebrafish Genome • The zebrafish genome has been fully sequenced to a very high quality. This has enabled scientists to create mutations in more than 14, 000 genes to study their function. For example: Mutations that disrupt embryonic development in zebrafish, serve as models for human diseases like muscular dystrophy, neurodegenrative diseases. • Zebrafish have 25 chromosomes. Zebrafish genome consists of about 1. 5 x 10 billion basepairs. Mammalian genome consists of about 3 x 10 billion basepairs. • Zebrafish share 70 per cent of genes with humans. 84 per cent of genes known to be associated with human disease have a zebrafish counterpart.

• more than 26, 000 protein-coding genes, the largest gene set of any vertebrate so far sequenced • Comparison to the human reference genome shows that approximately 70% of human genes have at least one obvious zebrafish orthologue (Orthologs are genes in different species that evolved from a common ancestral gene by speciation. Normally, orthologs retain the same function in the course of evolution. )

ZEBRAFISH Used for mapping and identifying genes involved in organ development. Excellent model for studying infectious diseases v REASONS§ Has most of the same organs found in mammals. Most human genes have homologues in zebrafish such as ATP-binding domains of kinases § Zebrafish embryos develop outside the mother’s body and are transparent throughout the first few days of life. § 14

Zebrafish Genome Found Strikingly Similar to Humans According to a paper published in Nature, 70 per cent of protein-coding human genes are related to genes found in the zebrafish (Danio rerio), and 84 per cent of genes known to be associated with human disease have a zebrafish counterpart.